a. Field of the Invention
This invention relates to systems for controlling power dissipated in fluorescent and other gas discharge lamps.
B. Description of the Prior Art
It is known to utilize a ballast having a winding in series with a fluorescent lamp, the purpose of the ballast being to serve as a choke to prevent excessive current flow in the lamp. Disadvantages of such a system are that a significant amount of power is lost in the ballast and the use of the ballast increases the initial cost of the lamp.
It is also known to control current flow in fluorescent lamps by using a variable impedence in series with the lamp and utilizing a feedback signal to vary the value of the impedence as lamp current changes. One disadvantage of this system is that a significant amount of power is lost in the variable impedence.
It if further known to use feedback signals to control power applied to apparatus such as heaters, where the feedback signal may be generated by a thermocouple or by a thermistor connected in a bridge circuit. While such systems can be used to control power application over a period of time, they cannot be used to control power on a cycle-by-cycle basis.